1. Field of the Invention
The disclosure relates to a Ravigneaux planetary gear device used for an automatic transmission of a vehicle or the like.
2. Description of the Related Art
In the past, a Ravigneaux planetary gear device has been proposed such as one in which a front sun gear and a rear sun gear are arranged on a center axis and a long pinion gear and a short pinion gear are arranged between the sun gears and a ring gear provided concentrically with the respective sun gears (for example, refer to Japanese Patent Application Laid-open No. 2005-325966).
In the Ravigneaux planetary gear device, gears whose lengths are different from each other such as the long pinion gear and the short pinion gear are provided. Accordingly, an engagement point of the gears becomes offset, whereby a force of moment is generated in each of the pinion gears during rotation. Additionally, there is a case where the force of moment is not balanced and a rotation axis (supporting axis) of each of the pinion gears is inclined.
Here, an end surface of a tooth of the pinion gear in the Ravigneaux planetary gear device is usually subjected to chamfering processing. A corner portion is formed on a boundary between a section subjected to the chamfering processing (hereinafter, referred to as chamfered portion) and a section not subjected to the chamfering processing (hereinafter, referred to as flat portion). Accordingly, when the rotation axis of the pinion gear is inclined as described above, the corner portion of the end surface of the gear makes local contact with a contact surface of a peripheral member (e.g., a washer, or a bearing) arranged adjacent to the end surface of the gear.
At this time, when the aforementioned contact surface of the peripheral member has a high friction coefficient due to deterioration of lubrication state caused by, for example, an insufficient amount of lubricant oil, part of torque received by the contact surface acts on, as a reaction force of torque, respective tooth surfaces of the pinion gears and other gears. As a result, a surface pressure applied to the respective tooth surfaces is made larger, making a load loss increase.